The geometry of propulsion nozzles for aerospace engines can be made variable by means of fixedly arranged wall elements on one side and variable primary and secondary flaps arranged opposite them on the other side. In this arrangement, a need exists for variable primary and secondary nozzle flaps and for fixedly arranged or adjustable wall elements alike to seal a clearance extending alongside the outer edges of the flaps and wall elements, respectively, relative to wall sections of a nozzle casing. A need often exists to seal a hot gas stream of the propulsion nozzle relative to the environment enclosed by the nozzle casing (pressure chambers) or relative to the atmosphere.
A clearance must also be provided between the fixedly arranged wall elements and adjoining nozzle casing walls to permit free expansion of the wall elements under differing service temperatures relative to the casing walls. The movable or variable flaps require means to bridge and seal the clearance, and allowance must be made for differential thermal expansion and for thermally induced wall distortions or warping.
In a conventional sealing means of the above type, primary sealing is achieved by means of a contact sealing effect produced exclusively by the differential pressure between the two chambers on opposite sides of the seal. Because of potential thermally induced distortions of a carrier of the seal in a slot and, thus, of the slot and the sealing element, the differential pressure required for the primary seal may not be safely developed at least in areas alongside the sealing clearance. In the worst case, the seal is made unserviceable by local jamming of the sealing element.